1. Field of the Invention
This invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device using a color filter formed in an ink-jet printing system and a process of fabricating the same.
2. Description of the Related Art
Generally, a liquid crystal display device, widely used as a flat panel display of active matrix driving system, divides a light generated at a light source into light of three basic colors, red (R), green (G), and blue (B), so as to display a color picture. To this end, the liquid crystal display device requires a red (R) filter for transmitting the red light only, a green (G) filter for transmitting the green light only and a blue (B) filter for transmitting the blue light only for each picture element (or pixel). The R, G and B filters must not overlap with each other in order to prevent the deterioration of the picture and the color spread.
Methods of fabricating such a color filter for the liquid crystal display device include the dye method, the pigment dispersion method, the electro-deposition method, the print method, etc. The dye method and the pigment dispersion method have an advantage in that they form a fine pattern; but have a drawback in that, since they need a photo-etching process for each of the R, G and B color filters, the fabrication process is complicated and wastes material. The electro-deposition method also has a drawback in that, since an electro-deposition and a mounting process for each of the R, G and B color filters is repeated, it causes a complication in the fabrication process. The print method has a problem in that it is difficult to uniformly control the thickness of the color filters.
Recently, in order to overcome problems in such existent color filter fabrication methods, there has been developed a method for fabricating a color filter using an ink-jet system. This method is capable of easily fabricating fine patterns using a relatively simple process. In the ink-jet color filter fabrication method, a color filter is formed by defining a lattice-type barrier rib for providing a cell area on a transport substrate and thereafter ejecting ink onto the cell area.
FIG. 1A is a plan view showing a color filter substrate in a liquid crystal display device with the conventional ink-jet color filter, and FIG. 1B is a sectional view of the color filter substrate taken along line 1B—1B in FIG. 1A. In FIGS. 1A and 1B, the color filter substrate includes a lattice-shaped barrier structure 2 provided on a transparent substrate 8, and a color filter 10 provided in a cell area 4 defined by the barrier structure 2. The barrier structure 2 is provided by forming a metal film such as Cr and the like or a black resin film on the transparent substrate 9 and thereafter patterning the film using photolithography, etc. This barrier structure 2 is intended to define the cell area 4 including the color filter 10, and is formed to overlap with gate and data wiring areas of a thin film transistor substrate opposed to the color filter substrate 8. The barrier structure 2 prevents the leakage of light and serves as a black matrix for absorbing external light, which increases contrast. The color filter 10 as shown in FIG. 1B is formed by injecting R, G and B inks into the cell area 4 and curing the ink. The color filter substrate 8 further includes common electrodes (not shown) over the barrier structure 2 and the color filter 10.
FIG. 2A is a plan view showing a thin film transistor substrate opposed to the above-mentioned color filter substrate, and FIG. 2B is a sectional view of the thin film transistor substrate taken along line 2B—2B in FIG. 2A. The thin film transistor substrate includes a thin film transistor, provided at an intersection between a gate line 12 and a data line 14, and a pixel electrode 16 connected to the thin film transistor. The thin film transistor consists of a gate electrode 12A protruding from the gate line 12, a source electrode 14A protruding from the data line 14, a drain electrode 14B connected to the pixel electrode 16, and an active layer 18 providing a conductive channel between the source electrode 14A and the drain electrode 14B. The pixel electrode 16 is positioned at the cell area defined by the gate line 12 and the data line 14 and is an ITO (indium thin oxide) electrode with a high light transmissivity.
A method of fabricating the thin film transistor substrate will be described below with reference to FIG. 2B. The gate line 12 and the gate electrode 12A are provided by depositing a metal material such as Al, Ta or Mo on a transparent substrate 20 and thereafter patterning the metal substrate. By fully coating an insulating material thereon, a gate insulation film 22 is formed. A channel layer 18 and an Ohmic contact layer 24 are provided by sequentially depositing an amorphous silicon layer and an impurity amorphous silicon layer on the gate insulation film 22 and thereafter patterning them. The data line 14 and the source and drain electrodes 14A and 14B are provided by depositing a metal material over the substrate 20 and patterning the metal material. Next, the Ohmic contact layer 24 exposed through the source and drain electrodes 14A and 14B is etched. A protective film 26 is provided by coating the entire substrate with an insulating material, and contact holes are defined by patterning the protective film 26. The pixel electrode 16 is providing by depositing a transparent electrode material on the protective film 26 and thereafter patterning the electrode material. This pixel electrode 16 is electrically connected to the drain electrode 14B via the contact holes provided in the protective film 26.
The conventional ink-jet color filter fabrication method as mentioned above has an advantage over other existent color filter fabrication methods in that the fabrication process is relatively simple because the color filter is formed by the ink-jet system. The liquid crystal display device with the conventional ink-jet color filter, however, has a difficulty in that an ink ejection time must be discretely or discontinuously controlled because ink is injected in each cell area 4 of the lattice-shaped barrier structure 2.